The crash at Hatfield on 17 October 2000 has fed five years of legal process that is still yet to be concluded.
Efforts to find a 'controlling mind' responsible for the crash - necessary to prove corporate manslaughter - floundered even before the trial began. In September 2004 judge Justice MacKay threw out corporate manslaughter charges against Railtrack successor Network Rail because of lack of evidence; Railtrack's former chief executive Gerald Corbett and its safety and operations director Christopher Lea also had health and safety charges against them dropped.
MacKay also quashed manslaughter charges and health and safety charges against Charles Pollard, director of the London north eastern zone of Railtrack.
The trial eventually began in January 2005 with three Railtrack employees and two employees of maintenance contractor Balfour Beatty facing charges of manslaughter and breaching the Health & Safety at Work Act. The Railtrack employees were asset manager Alistair Cook, area asset manager Sean Fugill and track engineer Keith Lea. The Balfour Beatty employees were regional director Anthony Walker and civil engineer Nicholas Jeffries.
Balfour Beatty was charged with corporate manslaughter and breaching the Health & Safety at Work Act, but Railtrack's successor, Network Rail, was only charged under the Health & Safety at Work Act.
After the prosecution case ended in July, the judge ordered the jury to find all of those accused of manslaughter not guilty.
No reason was given at that stage, although an explanation could emerge when Network Rail and Balfour Beatty are sentenced next month.
With the manslaughter charges dispensed with, Balfour Beatty announced that it would plead guilty to charges that it had breached the Health & Safety at Work Act.